Milk Protein Products:
Casein & Whey
Introduction
Currently, various types of casein and of whey protein
are widely used in food processing, due to:
� Provide foods with a specific nutritive value
Infant formula, the application of partially
hydrolyzed protein for people who have allergic
problem, boosting protein content in beverages &
biscuits
� Replace more expensive proteins
Protein-rich whey products can (partially) replace
skim milk in ices, desserts, beverages, etc
Introduction
� Provide a product with specific physical properties
The preparation of stable emulsions (salad dressings,
desserts)
Foam products (toppings, meringues)
� Make novel products
An increasing trend in the food industry is the
production of ‘manufactured foods’ from fairly pure
and durable components. Examples are cheese-like
sandwich spreads, coffee creamers, and meat
analogues.
Manufacture
The properties of the milk protein preparations may greatly depend on the pretreatment of the milk or the whey.
Heat treatment is required to kill bacteria & to inactivate enzymes.
Heating can cause denaturation � decreased solubility of serum proteins.
This content depends also on the extent to which fat globules have become covered with plasma proteins � hardly be removed from the protein preparation by the common purification methods.
Bacterial spoilage and plasmin activity can cause proteolysis.
Casein Manufacture
Casein preparations are made from sharply skimmed milk.
The heat treatment of the (skim) milk is such that very little serum protein becomes denatured.
Denatured protein ends up in the casein product.
Casein is most often accumulated by rendering it insoluble.
Various types of casein preparations: rennet casein, acid casein, caseinate, micellar casein.
Casein Manufacture
Rennet Casein
� The casein is rendered insoluble by addition of calf rennet,
followed by stirring at a temperature increasing to about
55°C.
� The fine syneresed curd particles so formed are separated
by centrifugation, washed with water, pressed to remove
moisture, and then dried, for instance, in a drum or a belt
drier.
� The resulting product is composed of calcium
paracaseinate–calcium phosphate, with some impurities.
� It is insoluble in water and has a high ‘ash’ content.
Casein Manufacture
Acid Casein
� Skim milk is acidified, while stirred, with hydrochloric acid
(mostly), lactic acid, or sulfuric acid, until the isoelectric pH
of casein (4.6) is reached.
� The casein then is insoluble.
� The temperature applied is quite critical. At a high
temperature large lumps are formed,which are difficult to
dry; a low temperature causes a fine voluminous
precipitate, which is hard to separate. The optimum
temperature is about 50°C.
� The process is continued as described for rennet casein.
Casein Manufacture
Caseinates
� Acid-precipitated casein can be dissolved in alkali (NaOH,
KOH, NH4OH, Ca(OH)2, and Mg(OH)2), and the resulting
solution can be spray-dried � Na-caseinate (the most
common product), K-caseinate, Ca-caseinate
� These products can be well soluble in water and be almost
flavorless — if the pH during manufacture was never
higher than 7.
� A combination of a high pH and a high temperature will
result in formation of some lysinoalanine, which is
considered undesirable.
Casein Manufacture
Micellar Casein
� This can be obtained from skim milk by microfiltration; the
product is generally called phosphocaseinate.
� When using a membrane of pore size 0.1 µm, by far most
of the casein is retained, whereas virtually all serum
proteins can pass the membrane.
� Diafiltration with water is used to further remove
dissolved substances.
� The micelles obtained appear to have properties close to
those of natural casein micelles, also after drying and
dispersion in skim milk ultrafiltrate.
Whey Protein
Whey may vary substantially in composition.
• Whey obtained in classical cheese making.
� It contains soluble components of milk, the
caseinomacropeptide split off κ-casein; active rennet
enzymes; starter bacteria; lactic acid; and some globular
fat, which generally is largely removed beforehand by
centrifugal separation.
� The acidity of the whey greatly varies with the type of
cheese made.
� The whey may have been diluted with water and/or
contain some added nitrate.
Whey Protein
• Whey with a high NaCl content.
� It is resulted from Cheddar-type cheese making or from the manufacture of rennet casein.
� This whey is low in fat content and contains no starter bacteria, nor lactic acid.
• Whey resulting from the manufacture of acid casein.
� The fat content is low and it contains no rennet or casein macropeptide.
� The pH is about 4.6, and it contains increased amounts of calcium and phosphate .
In all cases, about half of the protein in whey consists of β-lactoglobulin.
Types of Whey Protein Preparations
Whey Protein Concentrate (WPC).
� The name is generally used for preparations containing 35 to 80% ‘total protein.’
� The preparations with a low protein content are often called skim milk replacers.
� WPC is made of delactosed, desalted whey, which is concentrated about 10 x by evaporation, to obtain lactose crystals.
� The mother liquid then is desalted.
� Drying of the remaining liquid results in WPC.
� A considerable proportion of the nitrogen is NPN, generally more than 20%.
� To obtain a higher protein concentration and a purer
product, utltrafiltration is generally used.
� To make purer products, diafiltration can be applied.
� The liquid is commonly spray-dried and the resulting WPC
powders can be highly soluble.
� The part of the protein that does not dissolve because it is
heat-denatured greatly depends on the pH and the Ca2+
activity during heating.
� Adding Ca salts after heating requires a higher
concentration of Ca2+ to insolublilize the protein.
Whey Protein Isolate (WPI).
� The name is generally reserved for preparations in
which 90% (or more) of the dry matter consists of
whey protein.
� Preferably, the whey used for its manufacture is
relatively pure; it is even better to use a
microfiltration permeate of skim milk.
� WPI can be produced, like WPC, by ultrafiltration; at
least one diafiltration step then is necessary.
� Other methods such as ion exchange also could be used.
� The whey is acidified to pH 3.2, where the proteins
present are predominantly positively charged � sieving �
washing in alkali (pH 8) � desorption of protein � drying.
� The protein is for almost 80% β-lactoglobulin and some
15% α-lactalbumin; it contains little of the other serum
proteins. This composition markedly enhances gel forming
properties.
� Besides, the protein is almost fully devoid of lipids, which
is of advantage when using it for foam formation.
Lactalbumin
� Heating sour cheese whey to precipitate its protein and to recover it � precipitate is impure.
� It is pressed, usually salted, and sometimes matured.
� A similar process can be applied to yield denatured whey protein. Often, CaCl2 is added besides acid.
� The precipitate obtained is washed and dried, for example in a drum drier � ‘lactalbumin’.
� It contains hardly any proteose peptone, caseinomacropeptide, or NPN.
� The high lactose content and the slowness of drying are responsible for extensive Maillard reactions.
� ‘Lactalbumin’ is insoluble in water.
Properties
Rennet casein, ‘lactalbumin,’ and coprecipitate are preparations that are fully insoluble in water.
They are applied in solid-like products such as biscuits. They can also be used to make ‘texturized’ products in an extruder, or for dry spinning.
In almost all other products the protein to be used must dissolve.
Increasing viscosity � caseinates
Gelling agent � caseinates, whey protein
Emulsifier � caseinates, micelar casein
Foaming agent